Glass fiber strands are typically formed by attenuating glass filaments through bushing tips or orifices at the bottom of a heated bushing containing molten glass. The filaments are then passed across the application surface of an applicator where they are coated with a binder and/or size. The filaments are then passed within the groove of a gathering shoe, which is typically a grooved wheel or cylinder formed of a material such as graphite, where the filaments are combined into one or more unified strands. The strand or strands are then collected on a rotating drum or collet as a forming package.
In the past, it has been found advantageous to form the filaments and strand on a first forming level and to collect the thus formed strand on a second forming level. This double level operation has improved the quality of strand produced.
However, a major problem in the formation of quality glass strands remains in controlling the environment at and directly below the bushing. It is well-known that as the filaments are attenuated through the bushing at high speeds, typically ranging from about 2,000 to 20,000 feet per minute (609.6 to 6096 meters per minute), that air is aspirated downwardly with the filaments, thus producing a shortage of air at the bushing. This results in turbulent air flow in the area around the bushing as new air attempts to replace that air which has been lost by withdrawal from the bushing area with the attenuated filaments. The turbulent air flow around the bushing results in uneven air flow and thus uneven temperature conditions at the bushing. This combination results in uneven filament diameters being formed and even filament breakouts occurring, the filament diameters being directly affected by any viscosity change in the molten glass which itself is dependent upon any change in temperature. If the turbulence becomes severe enough, breakouts of the filaments can also occur from the air currents alone.
It is thus a primary objective of the present invention to provide for a more uniform flow of air in the region surrounding the bushing to thus improve both the air flow and temperature environments which are critical to the glass filament formation.
In U.S. Pat. No. 3,304,163, it has been suggested to locate air conditioning ducts on either side of the bushing and slightly spaced from it. These ducts direct air downwardly with the filaments as they are being formed. While this does increase the air supply in the region around the bushing, it does not provide for the non-turbulent air flow at the bushing which is desired.